In the offshore Arctic, the seafloor is subject to extensive scouring by ridges of sea ice. The ice moves through the soil with great power, particularly in waters between 60 and 140 feet deep. Pipelines must be placed in trenches below this scour activity, which may require trenches as deep as 25 feet for tracts in 100 feet of water. To construct these trenches with slopes that would stay stable for the duration of construction would require massive excavations. Such trenches are too deep for mechanical excavation shields to be practical for the full depth. Thus, the art is in need of an improved seafloor deep trenching technique.
Applicant is not aware of any prior art which, in his judgment as one skilled in the pipeline art, would anticipate or render obvious the novel technique of the present invention; however, for the purposes of fully developing the background of the invention, and establishing the state of the requisite art, the following is set forth: "Slurry Walls" by Petros P. Xanthakos, 1979, page 2.